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Trying to get 256 color mode working in win98 (think I might need a driver?)

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  • Timo W.
    replied
    Nice. Mind to share some pictures?

    Do they work in DOS, too, or are these pure Windows accelerators like those Weitek 9000 chips?

    Leave a comment:


  • bear
    replied
    Originally posted by Timo W. View Post
    Interesting, but that's just an ad. Did you ever see one of those cards in the wild?
    Yeah, enough to have added several to my collection, plus a few more I left for others. They're not very common, but I wouldn't say vanishingly rare. A bit tough to love, since they only ever had Windows 3.1 drivers (plus a beta NT driver that can be downloaded from the internet).

    Leave a comment:


  • Timo W.
    replied
    Interesting, but that's just an ad. Did you ever see one of those cards in the wild?

    Leave a comment:


  • bear
    replied
    https://books.google.com/books?id=eX...MgERLK&pg=PA55

    Leave a comment:


  • Timo W.
    replied
    No, never seen those for PCs.

    Leave a comment:


  • bear
    replied
    Originally posted by Timo W. View Post
    But the TGUI 9680 card he uses has no 3 MB option
    Fair enough.

    Originally posted by Timo W. View Post
    nor any other standard graphics card made for PCs.
    Did you know that SuperMac made the Spectrum/24 (with the 3 MB frame buffer) for PCs? In ISA, EISA, and VLB varieties, even. You can think of them as "non-standard" if you like. But they exist.

    Leave a comment:


  • Krille
    replied
    Have you tried looking for the same type of memory already installed on the card?

    Leave a comment:


  • J. Radon
    replied
    Originally posted by eswan View Post
    If the video card has empty ram sockets, you should be able to bring it up to 2 meg at least. Ought to be 2 pieces of 256k x 16 EDO SOJ.
    Is there anything else I need to know to ensure compatibility? I've been scouring eBay and this is the listing I'm currently looking at: https://www.ebay.com/itm/363154438656
    would something like this work?

    Leave a comment:


  • GiGaBiTe
    replied
    Originally posted by Timo W. View Post
    Not incorrect. You are wrong, as you just described AT, not ATX. What he said is 100% correct.
    I did not describe AT. Most ATX power supplies also have a physical on/off switch, just as AT power supplies did, but are usually controlled by the PWR_ON pin on the Minifit Jr. connector that goes to the motherboard. There are some systems that keep this pin shorted to ground at all times and rely on the AC power switch on the back of the unit for power control.

    https://i.imgur.com/72aWp5Ah.jpg
    https://i.imgur.com/TpmqsOWh.jpg

    Likewise, there were also AT systems that had soft power control. I worked on two such systems this year, one IBM tower and one Fujitsu FMVTowns. Both systems have a proprietary 3 pin connector and a bit of circuitry inside the PSU to enable soft power control.

    AT and ATX are not black and white standard differences, there was a lot of intermixing of both standards going on for a number of years.

    Leave a comment:


  • Timo W.
    replied
    Originally posted by bear View Post
    I'm going to expand on something Timo wrote. What he wrote is correct (except 3 MB is an option, just not a commonly used one - the SuperMac Spectrum/24, for example, has a 3 MB framebuffer) but you're not the first person here I've seen evidence some confusion about this kind of thing, so I'll try to spell it out in greater detail.
    Hehe, I know. I own a Mac with a 3 MB SuperMac Thunder/24 graphics card myself and even made a thread about it here:

    https://www.vcfed.org/forum/forum/co...permac-edition

    But the TGUI 9680 card he uses has no 3 MB option, nor any other standard graphics card made for PCs.

    Leave a comment:


  • bear
    replied
    I'm going to expand on something Timo wrote. What he wrote is correct (except 3 MB is an option, just not a commonly used one - the SuperMac Spectrum/24, for example, has a 3 MB framebuffer) but you're not the first person here I've seen evidence some confusion about this kind of thing, so I'll try to spell it out in greater detail.

    The video card needs to have memory to hold the pixels that are drawn on the screen. There are a lot of arrangements here; the simplest is the "linear framebuffer", which is essentially a region of memory that directly maps to the pixels on the screen. On a modern GPU-driven graphics card, this is a tiny fraction of the total available graphics memory. In the era you're looking at, basically the entire memory on the card is the framebuffer.

    The amount of memory needed for the framebuffer is a product of the number of pixels, and the number of bits needed to describe the color space.

    A black and white display needs one bit per pixel (it's either on, or it's off) -- you can fit eight pixels in one byte. So the amount of memory needed is the number of pixels, divided by eight. 1024*768*0.125 = 96 KB. Typically what you'd find in that case is a 128 KB framebuffer, as this simplifies the design, and the extra 32 KB becomes available as "off screen memory", which can be used to take advantage of the fact that it's often faster or more efficient to copy memory between different parts of the frame buffer, than to copy it between main memory and the frame buffer. So pre-rendered parts of the display font, or icons, or whatever else, can be drawn there, and then copied as needed into the part of the frame buffer that is visible on screen. Your modern GPU-based graphics cards still do exactly this, but on a much grander scale.

    With 4 bits per pixel (which can produce 2^4 colors, or 16), you can fit two pixels in one byte. So the amount of memory needed is the number of pixels, divided by 2. 1024*768*0.5 = 384 KB. Again, what you'll typically find is a 512 KB frame buffer, with 128 KB offscreen.

    With 8 bits per pixel (2^8 colors, or 256), one pixel fits in one byte. 1024*768 = 768 KB. Typically, a 1024 KB framebuffer with 256 KB offscreen.

    This is where the DAC starts to matter, and it's not just a question of the amount of framebuffer memory. Analog display adapters (such as VGA) use a DAC to convert the digital contents of the framebuffer memory into an analog color signal the monitor can use.

    1. The DAC defines how much total color fidelity you get - some early 256 color displays like the IBM PGC have a 12 bit DAC, which means it's possible to put 2^12 (4096) different colors on the display. You get to decide which 256 out of the total 4096, by programming the palette registers (a framebuffer memory cell is used to look up one of 256 12 bit color values from a lookup table (LUT), rather than describing the displayed color directly). VGA uses an 18 bit DAC, for 2^18 (262,144) possible colors, with the same kind of LUT arrangement. One of the "stupid tricks" of the VGA is to produce animations by leaving the image in the frame buffer alone, and just changing the color assignments in the LUT.

    2. The DAC also has a maximum bandwidth, which defines how fast pixels can be blasted out to the display. At a vertical refresh rate of 60 Hz, the DAC has 1/60th of a second (actually, a little less) to read all the displayable pixels out of the framebuffer. The calculations here are little more complex, but the short story is that this is why things happen like, some Matrox Millennium 2s with an 8 MB framebuffer, which is big enough to accommodate 1600x1200x32bpp, can't actually use that mode because the 220 MHz DAC is short of what's required. Some of them have 250 MHz DACs, though, which is enough, and the mode works on those cards.

    The LUT ("pseudo-color") arrangement for 8bpp and 12- or 18-bit DACs is no accident, if you consider both how it saves framebuffer memory, and the disadvantages of trying to represent an RGB color value directly using 8 bits. There's no way to split 8 bits evenly between each of red, green, and blue. So you end up having to decide: which gets short shrifted with only two bits of fidelity? R (RRGGGBB), G (RRRGGBBB), or B (RRRGGGBB)? Blue seems reasonable as the human eye is least sensitive to it, but whichever you choose, it makes for some quite obvious defects, e.g. trying to display shades of gray. Or do you restrict yourself to two bits for each (RRGGBB), which is evenly distributed but gives you only 2^6 (64) colors, and wastes the extra two bits? With the LUT, you are just referencing a value that does evenly divide by three (12 - 4 bits each for R, G, and B, or 18 - 6 bits each).

    That said:

    WIth 16 bits per pixel (2^16 colors, or 65536), one pixel fits in two bytes. 1024*768*2 = 1536 KB. But there is no LUT in this mode; the frame buffer memory location actually holds the color information directly ("direct-color"). So there is one extra bit of fidelity for one of R, G, or B. Most implementations gave it to green (R5 G6 B5, or RRRRRGGGGGGBBBBB), for human color perception reasons. But not all did. 15bpp doesn't have this problem, which gives it some advantages despite the lower total color fidelity. Since most memory bus arrangements are in multiples of 8 bits, actually implementing a 15 bit wide memory for a 15bpp display was not something that happened often (if ever at all) - they were pretty much all done in 16 bits with one "wasted". There's no LUT because there's no benefit: 16 bits of palette index uses the same amount of memory as 16 bits of color information, and 15 bits of color information is a pretty reasonable compromise, perception-wise.

    24 bits per pixel (2^24 colors, or 16,777,216), one pixel fits in three bytes (24 bits / 8 bits per byte). 1024*768*3 = 2304 KB (so you can see that 2 MB, or 2048 KB, is not enough). It gets a little awkward, because while some display adapters (like the Spectrum/24 I mentioned earlier) have their memory arranged in a way that makes it reasonable to have a 24 bit wide framebuffer, most boards had a 16- or 32- (or even 64- or more) bit wide framebuffer memory bus, which makes trying to store a 24-bit value either wasteful (of one byte per pixel) or inefficient (by "packing" four 24 bit pixels into three 32 bit memory words - 96 bits - known as "packed pixel"). The downside of packed pixel mode is if you want to manipulate a single pixel, you have to deal with four of them at a time, and the situation that each 32 bit word is going to contain different parts of two pixels. So there's computational overhead.

    32 bits per pixel makes the framebuffer design a lot more straightforward. One pixel fits in four bytes. 1024*768*4 = 3072 KB = 3.0 MB. You still get 2^24 colors, with the extra 8 bits either "wasted", or useful for other purposes (most commonly, an alpha channel, used to describe 2^8 (256) levels of transparency). Because of the overheads of packed pixel mode, a number of drivers offer "24 bit" modes which actually use 32 bits per pixel of framebuffer memory. This becomes noticeable with modes like, e.g. 1280*1024, which fits in a 4 MB framebuffer (3840 KB) using packed pixel, but not without (5120 KB). This is another reason, besides the DAC bandwidth, that a mode you might expect to be available... isn't.


    Probably people who are domain experts at this stuff are going to find plenty to nitpick in what I wrote. But I think it should do as a beginner's primer.
    Last edited by bear; June 9, 2021, 02:15 PM.

    Leave a comment:


  • J. Radon
    replied
    Originally posted by eswan View Post
    If you add ram, be carefull to get the orientation right. The chips will have a dimple in one corner that lines up with an arrow on the socket. They can fit backwards and will get really hot really quick and likely self destruct. Other than that, they just snap in easily.
    I already know about that, but I'm glad you point it out!
    It's something really easy to mess up if you aren't paying attention.

    I worked as a soldering technician for a while for a small company that made prototype cameras on commission for clients looking to mass produce.

    A lot of my work essentially boiled down to following board schematics and cross referencing it with the build order to populate components on small batch PCB's.

    Some of the components I had to solder on were BGA's, and because we didn't have an X-ray machine, I was essentially hand soldering them blind using a heat gun and hoping they worked.

    Needless to say, I prefer socketed chips and chips with exposed legs over BGA's any day. Nothing is worse than realizing you might've killed a $20 chip when you only have maybe 5 to work with and need at least one working board by the end of the day :c

    Leave a comment:


  • eswan
    replied
    If you add ram, be carefull to get the orientation right. The chips will have a dimple in one corner that lines up with an arrow on the socket. They can fit backwards and will get really hot really quick and likely self destruct. Other than that, they just snap in easily.

    Leave a comment:


  • J. Radon
    replied
    Originally posted by eswan View Post
    If the video card has empty ram sockets, you should be able to bring it up to 2 meg at least. Ought to be 2 pieces of 256k x 16 EDO SOJ.
    Oh yeah, look at that!
    I opened it up and sure enough it has two empty sockets on it.
    That's wild.

    I assume it wasn't too different from buying ram or any other memory component back in the day then?
    I know the bios is also on a removeable flash chip, but it's still kinda crazy to me seeing this sort of thing.
    The only experience I have with socket based memory chips is from a project I did years ago where I got a wilem serial port flash programmer to make a home made gameboy flash cart.
    I still have a ton of plcc 32 pin flash chips lying around.

    What kind of chips do I need to fill the slots out? I'll do some googling, but I assume they probably use some sort of common standard chip from the time?

    edit: i'm stupid, you literally listed the specs of the chips. "56k x 16 EDO SOJ"

    Leave a comment:


  • eswan
    replied
    If the video card has empty ram sockets, you should be able to bring it up to 2 meg at least. Ought to be 2 pieces of 256k x 16 EDO SOJ.

    Leave a comment:

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